The present invention relates to a chisel retaining device for a power operated percussion tool. In particular the invention pertains to a chisel retaining device of the type comprising a lock shell surrounding the chisel stem as well as the front end of the tool housing for axially locking the chisel relative to the housing.
The lock shell is pivotable between a closed and an open position.
In a prior art device of this type shown in U.S. Pat. No. 1,584,767 a lock shell is pivotably supported on the tool housing by two trunnious. The lock shell is lockable in its closed position by means of a separate lock pin which has to be removed from the shell to allow the latter to be moved to its open position. In this known device the impact forces to which the lock shell is exposed at no load strokes are transferred to the housing by the two trunnious which means that the trunnious as well as the lock shell have to be of a heavy and rather complicated design to withstand the occurring forces.
In another prior art device disclosed in U.S. Pat. No. 2,999,407, a lock shell is axially arrested relative to the tool housing as well as the chisel by means of toroidal lock springs inserted through apertures in the shell and received in peripheral grooves in the housing and the shell. Though this is quite a simple and rigid design it is rather awkward to handle at chisel replacements, because one or both of the lock springs have to be removed and reinserted. This is a time consuming procedure, especially when it has to be carried out in a cold and/or dirty environment.
The main object of the invention is to accomplish a chisel retaining device which offers in combination a safe protection against throwing out of the chisel at no load strokes and a simple and easy to handle constructive concept.
Other objects and features of the invention will be apparent from the following detailed description and the drawings.